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Synoptic-scale Weather Patterns and Large Slab Avalanches at Mt. Shasta California
Northwest Science
  • Cassandra Hansen, University of Nevada
  • S. Jeffrey Underwood, Georgia Southern University
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Upper atmospheric synoptic scale patterns associated with size-5 avalanches, the largest and most destructive types of avalanches, occur on Mt. Shasta, California in the Southern Cascade mountain range. We identified and analyzed fifteen size-5 avalanches over nine individual storm events in the last 50 years using composite and anomaly plots of surface and upper-air data and relationships between: 250hPa wind field, 500 hPa geopotential height field, 700 hPa precipitable water, atmospheric thickness, and surface temperature. Results indicated a strong correlation between synoptic scale warm air advection, moisture advection, strong southwest winds, and low geopotential heights and the formation of large, size-5 slab avalanches. The identification and orientation of a jet streak adds to the growing body of synoptic ingredients used for avalanche forecasting on Mt. Shasta.

Citation Information
Cassandra Hansen and S. Jeffrey Underwood. "Synoptic-scale Weather Patterns and Large Slab Avalanches at Mt. Shasta California" Northwest Science Vol. 86 Iss. 4 (2012) p. 329 - 341
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